The present invention relates to a technique for avoiding the occurrence of a fault in a mail gateway.
Nowadays, in communication by electronic mail (hereinafter referred to simply as mail), so-called spam mails unsolicited by recipients are transmitted in large quantity, emerging as a social issue concerning the Internet. (The term “spam mail” as used herein has the above definition, though varying depending on literature.) Communication common carriers managing mail servers such as Internet service providers (hereinafter referred to just as communication carriers) have been taking various measures for preventing the distribution of spam mails, e.g., spam mail filtering as a typical anti-spam provision.
An example of spam mail filtering is disclosed in U.S. Pat. No. 6,732,149. According to the disclosure contained in U.S. Pat. No. 6,732,149, there is described a technique wherein, in a first phase, a specific mail is determined to be an undesirable spam mail according to alert signaling from a user, and in a second phase, based on resultant data, it is detected whether each subsequent mail received is a spam mail or a variant thereof. Thus, mails that have been judged to be spam mails are filtered out to hinder undesirable reception or transmission of spam mails.
Besides the technique disclosed in U.S. Pat. No. 6,732,149, there are a variety of anti-spam techniques; for example, a technique for detecting peculiar characteristics of spam mails through machine learning, a technique for registering user-detected characteristics of spam mails into a database, and a technique for checking mails by calculating similarities to common-type spam mails or probabilities of spamming.